1. Field of the Invention
This invention discloses a multiple function sensing means for a fluid system. More specifically, this invention relates to a sensor for a vehicular coolant system. The sensor is a relatively compact structure to monitor under-pressure and over-temperature conditions in a coolant system, and provides a signal means indicative of a malfunction. Coolant can boil away at normal operating temperatures if the system is open, such as with a ruptured hose or a loose radiator cap.
2. Prior Art
Monitoring devices and sensors for fluid systems are known in the art, particularly temperature sensing apparatus for automobile coolant systems. There have been efforts to provide both over pressure and over-temperature sensing devices, but not an under-pressure and over-temperature sensor. Indicative of this prior art is U.S. Pat. No. 3,439,356 (Kinzer) which discloses a pressure-temperature sensor. In this apparatus opposed bellows chambers are coupled by a movable electrically conducting disc, which is displaced between a tube end and a thermocouple junction. The disc is moved to contact the thermocouple switch to energize a signal means and thereafter the disc is adjusted with a fluid at a known pressure to disclose an accurate pressure reading. The thermocouple is utilized in a known fashion to yield the temperature of a surrounding fluid.
U.S. Pat. No. 1,933,453 (Schlaich) teaches an indicating device responsive to both temperature and pressure. However, this device requires a coil resistor 13, a temperature coil shown as bimetal coil 16, and a diaphragm operator 24. The diaphragm operator 24 is responsive to an excess pressure to open a circuit. This device provides a current from a battery (not shown) to the end of resistor coil 13 and wiper 14 which is operable by diaphragm 24. The temperature actuation, although reasonably accurate at most temperatures, is inadequate to move the indicator for its entire distance or stroke. However, at an overheated condition sufficient for the liquid to boil vigorously, an excess pressure is disclosed that will actuate the diaphragm to move the indicator for substantially its entire travel range. A drawback noted in this device is, that until vigorous boiling occurs, the thermometer or temperature indicator does not accurately indicate the water temperature due to the difference between the water temperature and air temperature of the space surrounding the temperature responsive instrument.
U.S. Pat. No. 3,338,099 (Remick, Jr., et al) teaches a boiling point indicator which utilizes two sensors, one for pressure and one for temperature. A diaphragm operator moves a mechanical indicator. There is no teaching of an electrical signal provided for such readings. This particular device is operable only as an indicator of a safe-unsafe temperature.
U.S. Pat. No. 4,051,728 (Metz) teaches an instrument for monitoring a physical parameter, either temperature or pressure, utilizing an elastic sensor displaceable as a function of the monitored physical parameter. However, it is capable of only monitoring one parameter at a time. The device requires a belt having characteristics which change along the length thereof. The elastic sensor is responsive to the belt characteristic to produce an output signal which varies as a function of the physical parameter being monitored. Such a device is impractical for most automotive or vehicular usages.
Illustrative of early efforts at monitoring fluid bath temperatures in U.S. Pat. No. 1,815,642 (Zubaty) illustrating a bellows filled with a heat responsive fluid, which bellows is immersed in a fluid bath. A mechanical arm is connected between the bellows and a temperature indicator. As the fluid within the bellows is heated, the bellows is permitted to expand to move the mechanical arm and indicate the temperature. There is no teaching or consideration of pressure measurement.
Most vehicle coolant systems are operated at an elevated pressure which permits them to operate at a higher temperature. Generally these coolant systems are provided with relief valves to protect against an over-pressure condition. At a lower pressure the coolant will boil and evaporate from the system at a lower temperature. Therefore, it is vital to be forewarned of an under-pressure condition as well as an over-temperature condition in these coolant systems.
The above devices, which require immersion in or communication with a fluid to sense either over temperature or over pressure, do not provide a means for measuring both an over-temperature condition and an under-pressure condition. The under-pressure condition exists when the system fluid pressure is lost from a cooling system, such as through a loose radiator cap.